Distributed ion source acceleration column

Abstract

An ion beam system uses a separate accelerating electrode, such as a resistive tube, to accelerate the ions while maintaining a low electric field at an extended, that is, distributed ion source, thereby improving resolution. A magneto-optical trap can be used as the ion source.

1. An ion source for providing ions for a focused ion beam directed to a sample on a sample stage, comprising:
 a source region for containing supercold neutral atoms; 
 a source electrode on one side of the source region; 
 an extractor electrode on the opposite side of the source region from the source electrode, the extractor electrode having a hole, the source electrode and extractor electrode providing a source electric field having a source electric field strength across the source region; 
 an energy source for ionizing at least some of the supercold neutral atoms to create ions, the ions being accelerated by the source electric field through the hole; and 
 a resistive tube having different electrical potential along the tube for receiving ions from the hole in the extractor electrode and accelerating the ions. 
 
     
     
       2. The ion source of  claim 1  in which one end of the resistive tube is at substantially the same electrical potential as the extractor electrode and in which the other end of the resistive tube is at substantially the same electrical potential as the target. 
     
     
       3. The ion source of  claim 1  in which ions leaving the resistive tube are substantially collimated. 
     
     
       4. The ion source of  claim 3  in which the extractor electrode and the resistive tube together converge or diverge the ions to provide a positive or negative ion focal length of magnitude greater than 250 mm. 
     
     
       5. The ion source of  claim 3  in which the extractor electrode and the resistive tube together converge or diverge the ions or provide a positive or negative ion focal length of magnitude greater than 1000 mm. 
     
     
       6. The ion source of  claim 1  in which ions are accelerated in the source region and further accelerated within the resistive tube, the change in energy of the ions caused by the electric field in the resistive tube being at least 10 times the change in energy caused by the electric field in the source region. 
     
     
       7. The ion source of  claim 1 , in which the source region includes a magneto-optical trap for slowing and trapping the neutral atoms. 
     
     
       8. The ion source of  claim 1 , in which the resistive tube extends from within 5 mm of the extractor electrode and in a direction away from the direction of source electrode. 
     
     
       9. The ion source of  claim 1  in which the resistive tube comprises an insulating tube with a resistive coating. 
     
     
       10. The ion source of  claim 1  in which the extractor electrode and the resistive tube together converge or diverge the ions or provide a positive or negative ion focal length of magnitude greater than 50 mm. 
     
     
       11. A focused ion beam system, comprising:
 an ion source of  claim 1 ; 
 deflection electrodes for deflecting the ion beam extracted from the source region; and 
 a focusing lens for focusing the ion beam onto a sample on a sample holder. 
 
     
     
       12. The focused ion beam system of  claim 11  in which no beam defining apertures are positioned between the extraction electrode and the sample holder. 
     
     
       13. An ion source for providing ions for a focused ion beam directed to a sample on a sample stage, comprising:
 a source region for containing supercold neutral atoms; 
 a source electrode on one side of the source region; 
 an extractor electrode on the opposite side of the source region from the source electrode, the extractor electrode having a hole, the source electrode and extractor electrode providing a source electric field having a source electric field strength across the source region; 
 an energy source for ionizing at least some of the supercold neutral atoms to create ions, the ions being accelerated by the source electric field through the hole; 
 at least one acceleration electrode providing an extension electric field extending from the extractor electrode with the hole, the strength of the extension electric field just beyond the hole differing from the strength of the source electric field by less than thirty percent, thereby reducing or eliminating focusing effects as ions leave the source region. 
 
     
     
       14. The ion source of  claim 13 , in which the source region includes a magneto-optical trap for slowing and trapping the neutral atoms. 
     
     
       15. The ion source of  claim 13 , in which one of the at least one acceleration electrode comprises a resistive tube that extends from near the extractor electrode and away from the source electrode. 
     
     
       16. The ion source of  claim 15  in which the resistive tube comprises an insulating tube with a resistive coating. 
     
     
       17. The ion source of  claim 15  in which the electrical potential at the end of the resistive tube closest to the extraction electrode differs by less than 20% from the electrical potential of the extraction electrode. 
     
     
       18. The ion source of  claim 17  in which the end of the resistive tube closest to the extraction electrode is at about the same electrical potential as the extraction electrode. 
     
     
       19. The ion source of  claim 15  in which the system further comprises an ion focusing lens for focusing the ion beam onto the sample and in which the electrical potential at the end of the resistive tube furthest from the extraction electrode is at approximately the same electrical potential as the sample. 
     
     
       20. The ion source of  claim 15 , in which the at least one acceleration electrode comprises a series of electrodes and further comprising a voltage source for supplying decreasing voltages to the electrodes in the series as the electrode gets further from the source region. 
     
     
       21. An ion source for providing ions for a focused ion beam directed to a sample on a sample stage, comprising:
 a source region for providing ions; 
 one or more electrodes for providing an electrical potential at the extended source region; 
 an extractor electrode having a hole, the extractor electrode providing an electric field for extracting ions from the source region; and 
 an accelerating electrode having different electrical potentials at different points for receiving ions from the hole in the extractor electrode and accelerating the ions. 
 
     
     
       22. The ion source of  claim 21  in which the accelerating electrode is a resistive tube. 
     
     
       23. The ion source of  claim 22  in which ions leaving the resistive tube are substantially collimated. 
     
     
       24. The ion source of  claim 22  in which ions leaving the resistive tube are diverging. 
     
     
       25. The ion source of  claim 21  in which the accelerating electrode accelerates the ions over a distance greater than 5 times the size of the source region. 
     
     
       26. A focused ion beam system including an ion source in accordance with  claim 21 .